Prospective parents with high cholesterol levels could be in for a long wait to become pregnant, a new study published in the Endocrine Society's Journal of Clinical Endocrinology & Metabolism states.

According to the Centers for Disease Control and Prevention (CDC), high low-density lipoprotein (LDL), or "bad" cholesterol is a silent condition with no signs or symptoms that affects around 71 million Americans.

Of those, only 1 out of every 3 adults has the condition under control. While the body needs the waxy, fat-like substance to make and maintain nerve cells and to synthesize steroid hormones, in excess, it can build up on the artery walls leading to heart disease and stroke - the leading causes of death in the US.

The cohort study, "Lipid Concentrations and Couple Fecundity: The LIFE Study," comprises 501 couples, 18 to 40 years old, from 16 counties across Michigan and Texas recruited prior to conception in 2005-2009.

These couples were part of the Longitudinal Investigation of Fertility and the Environment (LIFE) study, which aimed to ascertain whether ever-present environmental chemicals in the context of lifestyle affect male and female fertility. Participants had discontinued use of any contraceptives - with the aim of getting pregnant - and were tracked daily for 12 months while attempting to conceive. Parents-to-be were followed monthly until delivery.

Study author Enrique F. Schisterman, M.S., Ph.D., of the National Institutes of Health's Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) in Bethesda, MD, says:

"In addition to raising the risk of cardiovascular disease, our findings suggest cholesterol may contribute to infertility."

"Our results suggest prospective parents may want to have their cholesterol checked to ensure their levels are in an acceptable range," he concludes.

Among the 401 (80%) women who completed the protocol, 347 (87%) became pregnant and 54 (13%) did not. Over the course of the study, 100 (20%) withdrew, most commonly due to a lack of continued interest in participation.

Couples with high cholesterol levels took longer to conceive

Researchers measured each couple's cholesterol at the initial stage of the study through blood samples. The four main categories - total cholesterol, LDL cholesterol, HDL cholesterol and triglycerides - are what are most commonly measured or calculated during a cholesterol test.

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Couples where either one or both had high cholesterol took considerably longer to become pregnant than those couples with cholesterol within the normal scale.

However, researchers in this study measured the total and free amounts of cholesterol in the blood sample.

Results indicate that those couples in which either one or both had high cholesterol took considerably longer to become pregnant than those couples with cholesterol within the normal scale.

"Couples in which both the prospective mother and father had high cholesterol levels took the longest time to conceive a child," says Schisterman.

"Our study also found couples in which the woman had high cholesterol and the man did not took longer to become pregnant than couples where both partners had cholesterol levels in the normal range," he adds.

The proportion of adults in the US with high levels of low-density lipoprotein cholesterol (LDL-C) who were treated increased from 28.4% to 48.1% between the 1999-2002 and 2005-2008 study periods, according to the CDC. Strengthening the use of preventive services through improvement in health care access and quality of care is expected to help achieve better control of high LDL-C in the US.

The LIFE study recently suggested lipid concentrations might affect semen quality, with higher levels of total cholesterol and free cholesterol associated with a significantly lower percentage of spermatozoa.

This study - together with an alarming report from Medical News Today that recently said 1 in 3 children may have high cholesterol - proposes a possible question mark against the future of fertility in the US, unless changes are made.